Bangladesh is the most densely populated country in the world, with very little in the way of material items. It is basically a huge delta, so has minimal native production capacity except for food. Most of it is rural, though most foreigners stay in Dhaka, the capital city of about 15 million people. Many people, especially kids, are involved in picking through waste and recycling collecting most everything imaginable (and more). Bangladesh has some very skilled repairers and bodgers who fix and recycle broken items that in other countries would get thrown away. Don't count on finding anything of value, far less anything edible in trash, unless you are a Bangladeshi yourself. There are a lot of hungry people and poor people in Bangladesh who probably need stuff a lot more than you!
That having been said, foreigners and those who live in the wealthier parts of Dhaka, such as Gulshan and Banani, do occasionally discard stuff randomly without understanding its value. For example, Robin has found useful trash in Banani and Uttara.